1. Field of the Invention
The present invention relates to a fuel injection device for supplying fuel by injecting it into the intake path of an engine, and specifically relates to a fuel injection device that is provided with a priming pump for loading fuel into the fuel passage leading to the injector during engine start-up, and that is further provided with a fuel return path for returning the gas and excess fuel accumulated in the interior to the fuel tank.
2. Description of the Related Art
Fuel injection devices that pressurize and supply fuel by injecting it into the intake passage of an engine are well known, as described, for example, in Japanese Patent Publication No. 2001-193610. As shown in FIG. 3, the device has a fuel pump 31 used for pumping fuel and connected with a fuel supply line 5 that extends from the fuel tank, a solenoid (injector) 32 used for injecting fuel and connected with a high-pressure fuel passage 37 extending from the fuel pump 31, and a constant-pressure chamber 33B formed medially along the high-pressure fuel passage 37 and used to adjust the fuel injection pressure at a constant pressure. Fuel is injected into the intake passage 10 with a predetermined timing so as to be supplied to the engine.
Thus, with this fuel injection device 3B, the fuel return passage 39 extends from the constant-pressure chamber 33B and is connected to the fuel return line 6 that extends to the fuel tank. In addition, a priming pump 34B is provided medially along the fuel return passage 39, so that the air accumulated in the high-pressure fuel passage 37, including the constant-pressure chamber 33B, is discharged manually to the fuel tank at the time of engine start-up, allowing fuel to be introduced all the way up to the solenoid valve 32, and the vapor or excess fuel accumulated in the constant-pressure chamber 33B to be returned to the fuel tank via the fuel return passage 39 at the time of engine operation.
However, with the fuel injection device 3B and other conventional fuel injection devices, the fuel return passage 39 is positioned below the constant-pressure chamber 33B, as shown in the drawing, producing a structure in which the air that has low specific gravity and accumulates at the top is difficult to remove completely. In addition, the vapor that has been generated by the heat of engine operation is also likely to accumulate at the top in a similar manner, which tends to create a situation in which discharge is difficult.
When driving is stopped after engine operation, the fuel tank is heated by the residual heat of the engine, and the fuel inside tends to reach high pressure. To allow the priming pump 34B to operate adequately in response to this high pressure, the spring pressure of a check valve is commonly set high, making it difficult to sufficiently discharge the accumulated vapor with the discharge pressure generated by the fuel pump 31.
The problem thus arises that the air, vapor, or other gas accumulated in the high-pressure fuel passage 37 of the fuel injection device 3B causes pressure fluctuation in the device, impedes the outflow of fuel during discharge, and hence has a variety of adverse effects on engine performance during the period in which the gas is discharged from the solenoid valve 32 to the intake passage 10.